External power supply VS USB

Using Arduino Motors, Mechanics, Power and CNC
1

Hello World,

Recently, I got a new 5 Vdc Power supply 3A to power my arduino uno + ethernet shield but there is something going on I cannt explain.

When I use the power supply to send signal to a 5vdc relay, it powers it up to it does not click ( common to N.O.) contact even though the led blinks, showing a change of state.

When I power it up with a USB from my computer it works fine...

I measured output voltage from the USB and power supply: both send 5 Vdc but it seems that the power supply is not to the taisk.

I also noticed that the on LED from ethernet shield is a lttle dimmed when powered by the external power supply.

Does this ring a bell to somebody?

Your comments are very welcome.

Thanks in advance. :o

2

Are you plugging the 3A power supply into the USB jack?
Is the power supply regulated?

3

Post a photo of a drawing of how you have everything connected. (It must be a drawing - however crude - not a photo of your Arduino)

...R

4

LarryD:
Are you plugging the 3A power supply into the USB jack?
Is the power supply regulated?

The power supply ( transformer) Input: 120 V AC 0.5 A
Output: 5 V DC 3 A

It comes with a 2.1 mm I.D. male jack connector, which I connect to the female jack connector of the arduino.

It´s a fixed one: Output: 5 V DC 3 A

Thanks,

5

The output current on the Arduino is limited to 40mA per pin. Is that sufficient to drive your relay? if your relay needs more current to switch, you need to power the relay externally or use multiple pins.

6

Robin2:
Post a photo of a drawing of how you have everything connected. (It must be a drawing - however crude - not a photo of your Arduino)

...R

Hi, Robin

It´s actually a very simple circuit.

What I´m doing is turning on & off a led using my arduino uno + ethernet shield.

I got a 4 channel relay stuff and the connection goes this way:

5 V Power pin from Arduino goes to Vcc pin of the Relay coil.
Ground Pin from Arduino goes to Ground pin of the Relay coil

and pin #2 from Digital pin goes to Signal pin of the Relay

So these are the cases:

Case#1

When powering the system using an USB cable that comes from a Laptop everything work put well...
The relay change state and you can hear a click from the Relay.

Also the leds from arduino and relay shine normally

Case #2

When powering from the power supply I just go:

Input: 120 V AC 0.5 A
Output: 5 V DC 3 A

I noticed that the led from the relay - the one that tells you when a channel is on or off - it actually turns on and off but there is not click from the relay and the lights from the leds are a little dimmed...

I took my multimeter and measure voltage from both cases ( #1 & #2) and both were 5 V DC

So my question are:

  1. Why there is not click in case #2 ?
  2. Is there any dangerous situations for the arduino and/or power supply?

Thanks in advance,

7

How is the PSU connected to the Arduino?

8

Riva:
How is the PSU connected to the Arduino?

You plug the PSU into the 120 V AC outlet and then in the other side it has a male jack connector that goes straight to the female jack connector of the arduino.

9

03ed:
Hi, Robin

It´s actually a very simple circuit.

In that case it will only take a minute or two to draw it. No amount of words is an alternative for a drawing.

It sounds like you are plugging a 5v power supply into the barrel jack on your Arduino.

The minimum voltage for that jack is 6v and the recommended minimum voltage is 7v. RTFM

...R

10

Robin2:
In that case it will only take a minute or two to draw it. No amount of words is an alternative for a drawing.

It sounds like you are plugging a 5v power supply into the barrel jack on your Arduino.

The minimum voltage for that jack is 6v and the recommended minimum voltage is 7v. RTFM

...R

Indeed I am.

I will swap with another PS with the recommended voltage and see what happen.

Thank you.